Forged car wheel



Aug. 1o, 1943.

R. B. DIMMlcK 2,326,127`

FORGED CAR WHEEL Original Filed May 4, 1940 INVENTOR. FALp/-f /MM/CK.

ATTORNEYSk Patented Aug.10, 1943 FORGED CAR WHEEL Ralph Dimmick, Bu'uer,Pa., assignent@ The American Rolling Mill Company, Middletown, Ohio, acorporation of Ohio Continuation of application Serial No. 239,691,November 9, 1,938, and a division of application Serial No. 333,355, May4, 1940. This application January 22, 1942, Serial No. 427,727

j Claims.

My invention relates primarily to a process of heat treatment of ferrouswheels for railroad rolling stock and the like and an improved wheelresulting therefrom. This application is acontinuationof my copendingapplication, Serial No. 239,691, led November 9, 1938, and is a divisionof my copending application, Serial No. 333,355,

flied May 4, 1940. I shall describe my invention tions are protectedfrom the quenching action and therefore remain soft, while the rim ishardened. While this procedure also results in a usable wheel, severalnew disadvantages are introduced which were not present in the uniformly.quenched wheel'previously described. Since only in connection withforged steel car wheels though .I

it is not necessarily limited thereto.

The fundamental object of my invention is the provision of a processwhich will simultaneously bring about the following conditions in thearticle: A

1) 'I'he tread of the wheel has suicient hardness to successfullywithstand difcult service conditions. v

(2) The hub is soft enough to permit easy machining.

A(3) The tensile and fatigue strength and the ductility of the plate ofthe wheel are very high, adding to its factor of safety. v l (4) Thewheel is free of dangerously high internal stresses.

The last -two of these considerations are, of course, the mostimportantsince above all the wheels must be safe. In my processthedesiderata above are coincidently achieved; andthis, so far as I know,is a wholly new aspect of utility which my product possesses.

In one prior process it is the practice to heat the wheels to above thecritical point and then the rim section of the Wheel has been quenched,the steel in the other parts of ,the wheel does .not get the benefit ofthe refining action on the microstructure which is afforded by a quenchand a draw, and consequently the strength andductility are inferior.Also as can readily be appreciated, this unequal quenching sets upexceptionally high stresses in the wheel. The equipment to. quench theentire wheel in a liquid, usually.

oil, and then uniformly to draw the temper of the entire `wheel torelieve the dangerously high quenching stresses. While this process hasresulted in a usable wheel, it is not all that could be desired inseveral respects. The chief undesira-ble feature is that when the wheelhas been heat treated to produce a degree of hardness in the rim whichwill satisfactorily resist dimcult service conditions, the hub is sohard -as to be very dimcult to machine; and the finishing of the borebecomes a very difficult and expensive for carrying out this process is,moreover, quite large and complicated and adds greatly to theinconvenience and expense' of the process. Following this differentialquenching operation it is customary to employ .a uniform drawto relievethe stresses somewhat and to improve the .physical properties of therim. The rest of 4the wheel is little affected by this draw since it hasnot been quenched. i

In my new process I avoid these undesirable features by providing(following an over-all quench) a differential draw or tempering in whichthe temperature difference between the hub and the rim is carefullycontrolled by a differential application of heat so that the hub isheated to a, high enough temperature to effectively soften it while therim is held at a. sufciwently low temperature to prevent unduesoftening, followed by an equalization of temperatures and a slowcooling. For the best combination of properties this differential drawis preceded by a uniform quench.

By following this procedure I produce a wheel having a combination ofmaximum rim hardness to resistshelling and wear, softness in the hub togive good machining properties, and controlled stresses 4to provide themaximum of safety in service. li

The ngure isv a sectional view through a type of draw furnace which Imay employ, showing also an exemplary heating means.

In practicing my preferred process the lwheels to be heat treated arefirst heated slowly in anperature. This procedure of heating prior tothe quench is Well understood in the art and the par. ticular heatingschedule is not critical for the achievement of my result.

The heated wheels are then quenched preferably in oil, althoughwater,brine, or other fluids are effective. It is preferred that thisquench be uniform over the entire wheel, that is, that no part of thewheel be protected from the rapid cooling action of the cooling medium.The principles and practice of quenching are also well understood in theart, and my invention does not contemplate the use of any particularmethod other than preferring a uniform quench. It is of courseunderstood that the quench should be carried out in a manner consistentwith generally understood metallurgical principles.

To accomplish the desired changes in microstructure it is only necessaryto cool rapidly to below the critical temperature; but additionaldesirable hardness is imparted to the wheel the lower the temperature towhich the wheel is quenched. This additional hardness is accompanied byincreased stresses. To avoid the formation of excessively high stressesand to avoid the possibility of forming so-call-fd shatter cracks, Iprefer not to quench to below around 450 F. For reasons of commercialexpediency the draw usually immediately follows the quench, and there isa saving in both heat and time if the wheel is placed into the drawfurnace while still quite hot from the quench. The quench must becontinued to a suiiciently low temperature, however, to give the desiredhardness of the rims, and to make.

possible, during the draw, the temperature differential between the hubsand the rims necessary to achieve my novel result, as will now bedescribed.

The wheels now have a microstructure refined throughout by the uniformquench. The entire wheel is hard and stressed, In my process I hubtemperatures.

of the wheels, as shown at 6. The purpose of these will hereinafter bedescribed. They may, however, be made of other substance, metallic ornon-metallic. For example, asbestos composition will serve.

A third wheel is placed upon the second in the way described, and so onuntil the stack is completed. A furnace charge usually comprises six orseven wheels in my practice. Thermocouples are inserted between the rimsso that their temperature may be accurately determined during thedrawing period. It is also advantageous to locate thermocouples in aposition to measure the Exemplary thermocouple connections are shown at'I and 8. The cables may be thought of as connected to visual orrecording instruments in a position of convenient access to theoperator. I

When the stack of wheels has been completed in the draw furnace aheating element is positioned in the space formed by the concentricbores of the wheels. A convenient form of heating element, and one whichI illustrate is an electrical resistance heater. In the figure, 9 repre-.sents the resistance element of such a heater,

held by suitable heat resistive and insulating supports I0. The terminalportions of the resistance element are brought out through a top brickspacer I I, which forms a closure for a hole in the cover 3, of thefurnace. If desired, a bottom brick spacer I2 may be employed, the twospacers being held together by a connecting rod I3, or other suitablemeans which passes through the several heater supports I0.

soften the hubs without unduly softening the rims and at the same timemodify internal stresses by adifferential draw which in its simplestform consists in heating the hubs hotter than the rims. In my preferredfurnace, which is illustrated in the drawing, this is accomplished bythe use of an internal heating means inserted within the bores of anumber of stacked wheels. An exemplary arrangement for my draw furnace.is illustrated in the figure. I prefer to employ a furnace which iscylindrical in form and of a diameter not much greater than the diameterof the wheels which are to be treated in it. On a suitable floor I, Imount a cylindrical casing 2 of insulating character. The casing may, ifdesired, be of such character as to be removable by a crane; and thearrangement of wheels may rst be made and then the casing lifted overit. Or if desired, the casing may be fixed in position and closed bymeans of a movable top member 3, also of insulating character. The carwheels are arranged in a vertical stack. The rst wheel is placed in thefurnace in a horizontal position resting on a suitable support. Thesecond wheel is placed on top of the first, care being taken to keep thebores of the wheels in alignment. Whenever the hubs are thicker than therims, as they usually are, I may employ spacers 5 between the rims tohold the wheels in a horizontal position. These spacers may convenientlybe made of cut sections of relatively heavy 4" or 6" diameter pipe, butmay also be made of other substance, metallic or non-metallic. A numberof these, usually three, are placed on the top of the rim of each wheeland equally spaced around the periphery thereof, before the next wheelis placed in position.

I also commonly employ circular collars, preferably of stainless steel,placed between the plates The heating element in this form is a unitarystructure to be inserted and withdrawn through the hole I4 in thefurnace top, and adapted to close the said hole when in position.

While an electrical heating element is most convenient and most easilycontrolled, I am not confined to the use of such means since other typesof heating devices can also be employed. A radiant tube type of heatercan be used with slight modification in the furnace to provide for theburner at one end and exhaust at the other. Also I find it advantageousto preheat the furnace, and sometimes to apply heat to the furnacegenerally, if that' should appear necessary. As a consequence thefurnace may be provided with electrical heating elements or burners forsuitable fuel and with a ue (notrshown). Or the interior of the furnacemay be arranged to be heated by circulation through it of hot gasesderived from a burner or burners or electrical heating elements locatedin a chamber externally of the casing 2.

In order to illustrate the method of operation of my process I willdescribe the treatment of a lot of railway wheels of the compositionspecified by the Association of American Railroads, Specication M-107which calls for carbon, .67 to .82 per cent, and manganese, 0.65 to 0.85per cent. These wheels are first heated and uniformly quenched as abovedescribed.

In order to obtain the optimum combination of rim hardness, hubsoftness, good physical properties in all parts of the wheel and lowinternal stresses made possible by`my method of heat treatment I selectthe proper draw temperatures for the rim and hub, determining the rimdraw temperature as follows:

time the steel is to be held at the draw temperature. For example, themore severe the quenching treatment the'higher the draw temperatureshould be to relieve the internal-stresses resulting from the quenching;the higher the carbon and manganese content the higher the drawtemperature may be without appreciable loss of rim hardness; and thegreater the desired relief from internal stresses the higher thedrawteinperature should be. In the case of a wheel of, say. 0.70 percent carbon and 0.70 per cent manganese which has been uniformlyquenched in oil and which is to have a Brinell hardness of at least 321(a customary rim hardness for wheels of this analysis) and internalstresses not exceeding 20,000 psi, as measured in the plate of the wheelby a method to be described later, I would use" a draw temperature forthe rim of 800 to.900 F. and hold this for about 12 hours. However, itis possible to use a higher draw temperature for a shorter length oftime, or a lower temperature for a longer time, within limits.

In order to obtain satisfactory machining properties in the hubs of suchwheels' I have found that it is necessary to keep the Brinell hardnessaccording to the preferred process already dey scribed, it is necessaryof course that the wheels at the start of the drawing operation be lowerin temperature than the selected drawing temperature for the rims, andthe lower this initial temperature at the time the heat is rst appliedto the hubs, the more readily can the desired temperature difference beattained.

f In the course of regular production, the draw furnace will naturallybe heated to the selected temperature for drawing the rims of the wheelsthereof below 270. This can be secured by draw.- ing the hub for atleast two hours at a tempera'- ture of `1050 F. or higher. limit to howhigh this temperature can go because the carbides begin to go intosolution as the temperature is raised, and an undesirable coarselamellar structure might result from the subsequent slow cooling.Preferably the draw temperature should be such that spherodization ofthe carbides occurs, thus leading to the optimum in machiningproperties. For the accomplishment of these objectives the hub should beheated to not over 1250 F. and I find that satisfactory results areobtained if it is held for three or four hours at 1100 to 1150 F.

My invention comprises supplying such means and devising the propercombination of temperatures and times as will achieve the fourfoldobject already recited, namely, sufficient rim hardness to resistshelling and wear, satisfactory machining properties in the hub, andgood physical properties throughout the entire wheel together with lowinternal stresses.

Having described the selection of the draw temperatures for the rim andhub portions of the wheels, one method of carrying out the inventionwill now be explained according to my process and with my preferredapparatus. The heated and uniformly quenched wheels are charged into thedraw furnace in the manner described, and the thermocouples placed forindication and regulation of the temperature of the hubs and rims. Theelectric element 9, where this type of heating means is employedv isthen inserted in the bore of the wheels and the power is turned on tobring up the hub temperature as rapidly as possible to the hub drawtemperature that has been selected according to the method described.

This rapid heating of the hubs is the special feature which makespossible the temperature differential between the hubs and rims when thewheels areheated as described in a heat treating mechanism such as thatshown in the draw-V ing. More specifically, my object is attained byVThere is a practical` when the preceding lot of wheels is removedfollowing the completion of the preceding cycle. The furnace will coolsomewhat during the charging of the next lot of wheels but it isunnecessary to cool it to room temperature before starting the drawingoperation on the next lot of wheels. As I ordinarily carry out myprocess, the wheels, after uniform quenching until they are at atemperature ofabout 450 to 700 F., are immediately placed in the drawfurnace and the draw furnace after closing the cover will usually leveloff at a temperature of about 600 to 700.' F. Under theseconditlons Ihave found that with one form of apparatus in which I have been'carrying out my process commercially, it ls possible to heat the hubsto their selected softening temperature without raising the rims abovetheir selected drawing temperature, provided that the heating means iscapable of dissipating at least 16, kilowatts of electrical energy, orits equivalent ifother forms of heating means are used. To provide amargin 0f safety I prefer to use as much as 20 kilowatts or more.

These values are for average conditions with wheels of say 36" diameterand standard `hubs of say '1" bore and with the use of radiation collarsaround the hubs as the wheels are charged If the wheels are hotter whenthe application of heat to the hubs is started it will be necessary tolapply this heat at a greater rate in order to soften the hubs Withoutunduly softening the rims.

After the hubs of the wheels in the charge of six or seven wheels havebeen heated to at least 1050 F. and held there for at least two hours asmeasured by the thermocouples on the hubs of the wheels, the power isshut off on the heating element andthe temperature of the hubs al' lowedto cool and preferably allowed to eq'ualize with the other parts of thewheels at the selected drawing temperature for the rims. In my preferredpractice the rims are never permitted to get above their proper drawtemperature at any time during the drawing operation and for thispurpose I employ a pyrometer controller attached to therim thermocoupleto shut off the power to the hub heating element if this should benecessary.

With my preferred apparatus it is advantageous to use the equalizationperiod and external heat is applied to heat the recirculated furnaceatmosphere when necessary to maintain the selected draw temperature forthe rim of the k wheels. Although the time may vary with other forms ofapparatus I find that, in general, it is advisable to allow at leastfour hours after the hub heating -element is shut off for theequalization to proceed.

At the conclusion of the drawing treatment the wheels are cooled slowlyin accordance with usual practice in order to avoid introduction ofinternal stresses by the unequal cooling rates in different portions ofthe wheels which would result if the wheels were cooled more rapidly. Itis customary to remove the wheels from the draw furnace at theconclusion of the draw period and place them in preheated brick linedpits or tunnels where they are closely piled or stacked and require from24 to 48 hours to cool to about 200 or 300 F.

The same result can be obtained by allowing the wheels to remain in thedraw furnace and shutting on? the heat while they cool to 200 or 300 F.This delays the use of the draw furnace for treating subsequent lots ofwheels and is a practice followed only rarely in actual plant operation,as when the entire heat treating unit may be shut down at the end of arun.

` I nd that wheels of the above composition treated according to mypreferred process as described, will have a rim hardness of at least 321Brinell and a hub hardness not over 270. Furthermore, when the internalstresses are determined by the so-called dyadic-circle or rosette methodas described in the Bureau of Standards Journal of Research, volume 10,1933 R. P. 559, and volume 15, December 1935, R. P. 851, and volume 19,October 1937, R. P. 1034, the highest stress measured in the plateportion is found to be not over 20,000 psi and in most cases will beunder 15,000 psi. This is amuch lower stress than that obtainable by anyother known methods of heat treatment which will produce hard rims andsoft hubs.

Another distinguishing characteristic of wheels heat treated accordingto my new process is the improved microstructure in the hub portion.This consists of a partially or completely spheroidized condition of thecementite particles as contracted with the lamellar pearlite found inwheels heat treated by other methods. Hubs of wheels that are uniformlyquenched and uniformly drawn will tend to have a microstructure offinely spaced pearlite lamellae because the cooling rate is generallynot great enough to produce martensite in wheels of the compositions incommon use. The hubs of wheels that are non-uniformly quenched byprotecting the hubs and sometimes also the plates from contact with thequenching medium, and are thereafter uniformly drawn, will have fairlycoarse pearlitelamellae` because of the slow cooling rate through thecritical temperature range.

Thus wheels heat treated by my process are not only readilydistinguishable by the spheroidized structure of the hubs but theypossess the desirable properties that accompany such a structure amongwhich are good -ductility and impact resistance, high tensile andfatigue strength, and very satisfactory machinability.

My method thus produces a Wheel with a ,rim

'section of sumcient strength and hardness to withstand severe serviceconditions, which at the same ltime has ahub soft enough to be readilymachinable, has a desirable microstructure and physicalproperties, andis very low in internal stresses.

It will be understood that the showing of the heat treating apparatus isonly diagrammatic an-d 4that the description which has been given of theprocess is only exemplary and that the invention is capable of manyrei'lnements'wihich f will readily occur to those skilled in the art.For

iixed to the base so that the wheels are charged by slipping the boresover the heating means. The diameter of the heating means may be variedaccording to the size and mass of the hub's. Special precautions such asdampers in the reclrculating system, if such is used, enclosures at topand bottomv of the chimney formed by the stack of hubs to restrictconvection currents, and extra tight sealing of removable furnace coversif such are used, may be necessary in order to get the -desiredtemperature differential between the hubs and the rims of some wheels.Although i-t will generally be found advantageous to use the circularcollars 6, in some cases the required difference in tempera-ture betweenthe hubs and the rims can be obtained by rough machining the faces ofthe hubs if they are not already smooth enough from the rou-gh forgingso that' they can be piled to res-t hub 'to hub and thus prevent theradiation of heat from the heating means through any open space betweenthe hubs and adjacent wheels, as would occur if the wheels weresupported b'y spacers placed on the rims as shown in the drawing. If thehubs are Atightly enclosed, .by meansof circular collars or by beingplaced hub to hub and'by closing the top and bottom of the chimneyformed by the stack of hubs, it is possible and may -be desirable toextract heat from the rims during the hub softening part of the cycle byproviding for the circulation of the furnace atmosphere around them andcooling it if necessary by the use of cooling coils or other means,either in the furnace walls or externally.

Ordinarily the rims are allowed to come up to a certain temperatureduring the drawing operation and then are maintained at this temperatureduring the equalization period; but for some Wheels of special design itmay be necessary to allow Ithe rims to heat for a short time to atemperature above their desired draw temperature so that the hubs mayb'e heated suciently to soften them. Then after the hub treating meansis shut off the rims are brought back to their desired draw temperatureas quickly as possible by the recirculation of the furnace atmosphere.Such minor variations of my process can be made Without departing fromthe spirit of the invention, and I intend, therefore, to be limited onlyas indicated by the scope of the following claims.

Having now fully described my invention, what I claim as new, and desire-to secure by Letters Patent, is:

l. A low stress forged steel car wheel of integral character and uniformcomposition throughout, comprising a hub, a plate, and a rim, said wheelbeing characterized by a. spheroidized cementite structure in the hubportion thereof,

prising a hub, a plate, and a rim. said wheel being characterized by a-Br-inell hardness of at least 321 in the rim portion, a' Brinellhardness not in excess of 270 in the h-ub portion, and in which theinternal stresses in the plate portion, as determined by the dyadiccircle method, do not exceed 20,000 psi.

- 3. A low stress forged steel car wheel of integral character anduniform composition throughout, comprising a hub, a plate, and a rim,said wheel being characterized by a sphecementite structure 'in the hu-bportion thereof,`

and by a ne lamellar pearlite structure in the rim portion thereof, saidwheel being further characterized by a relatively hard rim portion, arelatively soft hub portion. and a high strength plate portion, andhaving a. Brinell hardness of at least 321 in the rim portion, and aBrineli hardness not in excess of 270 in the hub portion.

5. A forged steel car wheel of integral character and uniformcomposition throughout, comprising a. hub having a. spheroidizedcementite structure, a plate, and a lrim, said wheel being characterizedby a Brinell hardness of at least 321 in the rim portion, a Brinellhardness not in excess of 270 in the hub portion, and in which theinternal stresses in the plate portion, as determined by the dyadiccircle method, do not exceed 20,000 psi, the rim of said wheel having a.ne lamellar pearlite structure.

' RALPH B. DIMZMICK.

